def isprime(a):
    for b in range(2,int(a**(1/2))+1):
        if a%b==0:
            return False
    return True
digits ={
    "zero":0,
    "one":1,
    "two":2,
    "three":3,
    "four":4,
    "five":5,
    "six":6,
    "seven":7,
    "eight":8,
    "nine":9,
}
n=input().split(" ")
r = ""
j=0
k=0
for i in n:
    if i in digits:
        r=r+str(digits[i])
    else:
        print("Wrong input")
        exit()
r = int(r)
for l in range(r, r*1000):
    if isprime(l):
        j=l
        break
for z in range(r,2,-1):
    if isprime(z):
        k=z
        break
if r-k>j-r:
    print(j)
else:
    print(k)